In recent years, to achieve a high integration and a high performance of a semiconductor device, an etching to form a pattern having a high aspect ratio, and an etching to form a hard mask having a large thickness are required.
For this reason, when the hard mask is to be etched with using a mask of a photoresist patterned by lithography, the selectivity between the photoresist and the hard mask may be insufficient, so that the hard mask may not be etched. On the other hand, if a photoresist to be patterned by lithography is thick, the focal depth of the lithography is not likely to fit, so that an exposure may be disabled, which makes it impossible to pattern the photoresist. In order to resolve this problem, for example, a stacked mask process (SMAP) method is used.
In the SMAP method, a pattern formed in a photoresist is transferred to an intermediate film made of silicon oxide or silicon having a thickness of about 50 nm. In this case, since the thickness of the intermediate film is as small as about 50 nm, the pattern can be transferred before the photoresist is lost. The pattern is then transferred to a carbon film which is a lower layer having a thickness of about 300 nm and formed by coating, chemical vapor deposition (CVD) or the like, by using the intermediate film as a mask. At this time, if the intermediate film and the carbon film are etched by reactive ion etching (RIE) using a gas containing O2, N2, and H2 as main components, the selectivity can be increased. Therefore, it is possible to transfer the pattern to the carbon film having a large thickness. In this way, the pattern can be transferred to a hard mask of a lower layer of the carbon film, by using the carbon film where the pattern is transferred and having a large thickness as a mask. In addition, the carbon film can be removed through ashing, if necessary.
If the multilayered structure such as that in the SMAP method is used, it is possible to transfer the pattern to the hard mask. In such a case, however, since the number of stacked layers increases, the number of processes increases and a manufacturing cost increases.